Orthodontic brackets represent a principal component of corrective orthodontic treatment devoted to improving a patient's occlusion. In orthodontic treatment, an orthodontist affixes brackets to the patient's teeth and engages an archwire into a slot of each bracket. The archwire applies corrective forces that coerce the teeth to move into their aesthetically correct positions. The types of tooth movement desired during orthodontic treatment may vary significantly from the early stage of treatment to the final stage of treatment. The different types of tooth movement desired necessitate fundamentally different approaches for engaging the archwire within the archwire slot.
Self-ligating orthodontic brackets have been developed to eliminate the need for separate ligatures to secure the archwire to the bracket. Self-ligating brackets rely on a movable portion or member, such as a latch or slide, to retain the archwire within the bracket slot.
During the early stages of treatment, a clinician may use an archwire that does not substantially fill the archwire slot. The archwire may, therefore, not be fully seated in the archwire slot during treatment. That is, there may be space between the archwire and two or more opposing surfaces of the archwire slot and/or between the archwire and the movable member. This is often referred to as “passive ligation.” As a result, the archwire may slide or move relative to the bracket in the mesial and/or distal directions, in the labial and/or lingual directions, and/or in the occlusal and/or gingival directions during treatment. Thus, passive ligation may allow gross movement of the teeth. Considerable movement between the archwire and the bracket is possible. It will be appreciated that a relatively small archwire, which may be round in cross section, may be used to facilitate passive ligation and thus provide quicker leveling and aligning of the teeth during an initial stage of treatment.
During a later stage of treatment, it may be desirable to more precisely control the orientation of one or more of the teeth. In this regard, the archwire may be forcibly held or fully seated in contact with the archwire slot by the clip and/or optional ligatures to provide control of rotation on the particular tooth. This is often referred to as “active ligation.” The clinician may use a relatively large archwire, which may be rectangular as opposed to round, to substantially fill the space within the archwire slot. The larger archwire may then contact both the slot and the clip at the same time to enhance the clinician's control of rotation of and torque on the tooth.
While such self-ligating brackets are generally successful in achieving their intended purpose, there remain some drawbacks. By way of example, in some instances controlling the rotation of the teeth, such as near the finishing stages of orthodontic treatment, can be problematic. While there may be several factors that cause a reduction in rotational control, it is believed that one of the major causes is the loose fit of the archwire within the archwire slot of the bracket when the movable member is closed. When the movable member is closed, the bracket body and the movable member collectively form a closed lumen for capturing the archwire. A close fit between the lumen and the archwire is believed to be important for achieving excellent rotational control during orthodontic treatment.
The close fit between the archwire and the archwire slot when the movable member is closed may be affected by several factors including, for example, the tolerances of the manufacturing process used to form the bracket body and the movable member. When the orthodontic bracket is assembled, the various tolerances may “stack up” so as to provide a relatively loose fit between the archwire and the closed lumen provided by the bracket body and movable member. As noted above, such a loose fit is believed to result in a diminished capacity to control the rotation of the teeth.
Thus, while self-ligating brackets have been generally successful, manufacturers of orthodontic appliances, such as, archwires, continually strive to improve their use and functionality. In this regard, there is a need for orthodontic archwires that provide improved rotational control during orthodontic treatment, such as during the finishing or active stages thereof.